* {
    padding: 0;
    margin: 0;
}

.container {
    width: 600px;
    height: 600px;
    background: blue;
}

.container header {
    height: 100px;
    background: #998833;
}

.container section {
    height: 400px;
    background: #FE8;
}

.container section:hover {
    background: #987;
}

.container section::before {
    content: 'hello world';
    position: absolute;
    width: 100px;
    height: 100px;
    background-color: yellow;
}

@media screen and (max-width: 500px) {
    .container section {
        background: #901;
    }
}
